Method and apparatus for printing electrically



R. M. SCHAFFERT Nov. 20, 1951 METHOD AND APPARATUS FOR PRINTING ELECTRICALLY Filed Oct. 21, 1948 2 Sl-IEETS-SHEET l FiGURE 3 INVENTOR Roland M Schufferr FIGURE l Nov. 20, 1951 R. M. SCHAFFERT 2,576,047 1 METHOD AND APPARATUS FOR PRINTING ELECTRICALLY Filed Oct. 21, 1948 2 SHEETSSHEET 2 FIGURE 2 INVENTOR Roland M. Schoffert Patented Nov. 20, 1951 METHOD AND APPARATUS FOR PRINTING ELECTRICALLY Roland M. Schaifert, Columbus, Ohio, assignor, by mesne assignments, to Battelle Development Corporation, Columbus, Ohio, a corporation of Delaware Application October 21, 1948, Serial No. 55,816

6 Claims. (Cl. 101-426) This invention relates to a method and apparatus for printing or making multiple copies by the transfer of ,an electrically controlled developer powder from an insulating nonconducting image layer to a strip of transfer material, and has for its purpose to afford an apparatus by which any number of copies may be produced by such process at high speed in a practical and efiicient fashion.

The invention pertains to the process of producing copies according to which an electrically insulating or nonconducting image layer is charged electrostatically and dusted with a developer powder which is then transferred and fixed to a sheet of transfer material, and has for its purpose to afford a procedure and mechanism by which said process can be carried out for printing from such an image to produce any number of copies accurately and speedily.

More specifically, the invention has for its purpose to afford mechanism embodying a continuously rotating drum on which an electrically insulating or nonconducting image layer can be secured, means for continuously effecting a flow of developer powder over the image layer, means for feeding a transfer strip against the image layer and drum as the latter rotates, and electrostatic charging means for spraying a charge on the transfer strip to provide a charge for recharging the image layer and to effect transfer of the developer powder from the image layer to the transfer strip, the charging means also functioning to hold the transfer strip against the drum as a result of electrostatic action as it is fed thereby.

Another object of the invention is to afford mechanism that enables the feeding of transfer material in a path adjacent to a portion of the periphery of a drum carrying an insulating image layer, repeatedly transferring a powder image from the image layer to the transfer material, and aflixing each powder image to the transfer material as the latter travels through the machine.

An additional specific purpose of the invention is to afford practical and efficient means for applying the developer powder to the electrically insulating r nonconducting image layer on the drum so as to insure continuous and uniform distribution of powder over the image layer.

To these and other ends, the invention consists in the method and structure that will appear clearly from the following description when read in conjunction with the accompanying drawings,

2 the novel features being pointed out in the claims at the end of the specification.

In the drawings:

Fig. 1 is a perspective view showing a printing apparatus constructed and arranged to operate in accordance with one practical embodiment of the invention;

Fig. 2 is a diagrammatic side elevation, partly in section, and

Fig. 3 is a perspective view of a modified form of electrostatic charging mechanism.

Referring more particularly to the drawings in which like reference numerals refer to the same parts throughout the several views, designates a drum or cylinder that is suitably mounted on a shaft 2 supported and arranged to rotate in a frame 3 mounted on a base 4, the shaft 2 and drum I being driven from an electric motor 5 through any suitable reduction gearing 6 and belt 1 connected to a pulley 8 mounted on the shaft 2, the motor 5 operating to turn the drum in a counter-clockwise direction, as indicated by the arrow in Fig. 2.

Mounted on the drum 1 is a printing element or plate 9 in the form of an electrically insulating or nonconducting image layer which is carried by a sheet of any suitable flexible metal or other conductive material that enables its being flexed around and attached to the drum, the plate being secured to the drum in any of the conventional ways of attaching a printing plate to a supporting cylinder or drum as by means of suitable clamping devices, the backing plate of the image having, however, a good electrical connection to the electrically grounded drum, which it is deemed unnecessary to show.

The printing plate 9 with the insu ating or nonconducting image layer may involve any suitable conductive support provided with a layer of electrically insulating or nonconducting material thereon, which is electrostatically charged to receive a developer powder and thus form a powder image that is subsequently transferred to a strip of transfer material during rotation of the drum I, and the printing plate may consist of a support of metal foil or other thin conductive backing that can be readily positioned around the drum and attached thereto together with a coating or layer thereon that conforms to the image to be printed and constitutes the image layer.

The printing plate may be made by writing or tracing the desired design or subject on a metal plate with an insulating or nonconducting lacquer or paint, or the electrically conductive backing plate may be coated with a light-sensitive lacquer which the image area is produced by dissolving the unexposed portions of the sensitive layer and burning or otherwise fixing the image portion; a plate including a photoconductive insulating or nonconducting layer may have a powder image produced thereon by electrostatic charging, exposure, and powder development, after which the powder image can be made into a permanent printing image by fusing the developed powder image onto the plate which can then be fastened to the rotatable drum i, as already described; or the printing plate may be constructed in any other manner so as to provide an electrically conductive backing or support which lies against the rotating drum, and an electrically insulating or nonconducting image layer which continuously receives successive electrostatic charges and deposits of developer powder as it is flowed thereover, following which the powder image is transferred to a traveling transfer material and afllxed thereto in the manner that will now be described in more detail.

The drum is grounded by conductor I0, and

the developer powder is preferably flowed over the image layer by gravity, and to accomplish this there is provided a powder discharge receptacle ll having a movable cover 12 through which powder may be-filled into the receptacle and an inclined bottom or outlet l3 located adjacent to a portion of the periphery of the drum on one side thereof above the center, so that as the drum rotates counterclockwise, the developer powder will fall onto the image layer and move downwardly thereover by gravity in a continuous stream, thus being evenly distributed over the image layer. The receptacle II and discharge outlet i3 extend across the width of the image layer, as will appear from Fig. 1, and I4 is an extension on the receptacle l I which acts to conflne the powder as it leaves the receptacle and prevent its movement over the drum except downwardly over the image layer.

As the developer powder travels downwardly, the surplus powder which does not adhere to the image layer falls into a receiving receptacle l5 below the drum and .at the same side thereof, while [6 designates a wall leading from the receiving receptacle l5 to the bottom of the discharge receptacle I I, affording a compartment or housing around the side of the drum over which the powder travels. The developer powder is thus completely retained within the housing as it moves downwardly from the discharge receptacle to the receiving receptacle l5 which is provided with a suitable door I! from which the powder can be removed as desired for re-use. It will be understood that any other convenient structure may be employed for applying developer powder to the image layer on the drum either by permitting it to flow downwardly in a continuous stream by gravity from a point near the top of the drum or in other suitable fashion.

The powder image that is formed on the image layer in a manner that will appear clearly presently is transferred to a transfer strip of suitable material such as paper, as indicated at l8, which is fed from a suitable feeding roll i9 mounted on a shaft supported in the frame, and travels through a path adjacent to a portion of the periphery of the drum l and the image layer, as indicated in Fig. 2, said path and the feeding roll I9 being located on the opposite side of the drum and in spaced relation to the powder applying area already described.

The transfer strip is deflected away from the drum by suitable stripping flngers'2l mounted on a bar 22 and preferably adjustable endwise thereof, the transfer strip traveling thence downwardly over an inclined chute 23 onto a receiving roll 24 mounted adjacent to the lower end of chute 23. The receiving roll 24 is mounted on a shaft that carries a pulley 25 that is engaged by a crossed belt 26 driven by pulley 21 on a shaft 28 that is operated by belt 29 from the aforementioned reduction gearing 6, thus driving the receiving roll 24 for the transfer strip in a clockwise direction, referring to Fig. 2, to wind the transfer strip or paper thereon after it leaves the rotating drum and after the powder image is aflixed thereon.

In order to charge the image layer 9 electrostatically and to hold the transfer strip l9 against the drum while effecting its travel along with the drum while in contact therewith, there is provided an electrostatic charging means'comprising corona discharge needles 30 mounted on a bar 3| supported on and insulated from the frame by means of blocks 32 and connected by conductor 33 with a suitable source of current supply, said electrostatic charging means acting to spray a charge onto the paper or transfer sheet sufficiently large to overcome the adhesion of the powder particles to the image area of the plate and establish a greater tendency of the particles to adhere to the paper, and in this manner effect transfer of the powder image from the image layer on the drum to the transfer sheet I 8 while at the same time holding the transfer sheet by electrostatic attraction against the surface of the drum until it is stripped therefrom by the fingers 2|, as described in the copending application of Lewis E. Walkup and Donald L. Fauser, Serial No. 57,962, filed November 2, 1948. As is well understood, all matter consists of a balanced array of positive and negative charges. The nonconductive image exists in this balanced condition before it is charged; after charging it contains a superior charge of one polarity, in this case positive, although it may be either positive or negative. This superior positive charge attracts and holds the oppositely or negatively charged powder. When the corona charge is applied to the back of the paper, the powder is attracted to the paper and since the paper has a positive charge superior to that of the image, the image charge having been dissipated slightly by bleeding to the powder, air, and possibly to the backing plate through imperfections in the image layer, the charge on the paper attracts some of the negative charge from the balanced array in the nonconducting image. When the superiorly positively charged paper is then stripped from the image, it carries with it the attracted negatively charged powder, and, in addition, some negative charges from the balanced array in the nonconducting image. The subtraction of a number of negative charges from the image leaves the image with an excess positive charge, that is, the image is recharged positively. This phenomenon will cause the charge to build up on the nonconducting image on the first cycle to a limiting charge condition, and no increase in image charge is obtained beyond this limit in successive cycles. The mechanism described is therefore capable of maintaining the image charge at a fixed value indefinitely to make up for the leakage of the charge from the nonconductin image layer to round.

The charge applied to the insulating or non- 5, conducting image layer from needles is of opposite polarity to the charge on the developer powder, which is therefore attracted to and retained by the charge on the image layer to form a powder image that is transferred to the paper strip by electrostatic attraction and subsequently aiiixed thereto. If desirable to employ additional image layer charging means, a charging unit including corona discharge needles 34 mounted on a bar 35 supported by and insulated from the frame and connected by conductor 38 with a suitable source of current supply may be arranged as shown at the top of the drum, and acting to spray a charge onto the image layer having the same polarity as that sprayed by needles 30, supplementing the action of the latter and insuring a charge on the image layer to a potential suitable ior image development, while 34 designates charging needles mounted on a bar 35 located at the bottom of the drum and connected by wire 36 with a source of current supply having a polarity opposite to that of the current supplying needlestt and 3d, and acting to spray an addi tional charge on the powder and thereby increase the charge on the powder image if desirable heiore it reaches the transfer needles 30.

at designates heating elements of any suitable construction located beneath or otherwise in operative relation to the chute 23 and acting to fuse the powder image onto the transfer sheet as the latter travels downwardly over the chute 23. 38 designates a cleaning means arranged to engage the insulating image layer on the drum after it leaves the transfer strip and to remove any powder adhering to the image layer which has not been previously transferred to the paper strip, thus preparing the image layer for a fresh supply oi. powder. It will be understood that the cleaning means 38 may consist of any suitable wiping instrumentality extending across the image layer of the drum, a suction device, brush, air blast, or other means that would be efiective to remove adhering powder from the imagelayer before the latter is again subjected to a powder dusting operation.

"In order to insure thorough cleaning of the drum after each transfer operation, additional charging needles 44 may be provided, mounted on bar 45 and connected by conductor 46 with a source of current supply having a polarity opposite to that sprayed by the needles 30, the needles ill spraying a charge which acts to loosen any powder adhering on the drum after the transfer operation by neutralizing the charge on such powder.

The electrostatic charging means which are preferably in the form of corona discharge elements including the needles such as 30 and 34 are supplied with a high potential electric current through their respective conductors, resultin in a charge that is sprayed onto the insulating image layer and drum, the current passing through the drum and such areas of the printing plate 9 as do not carry a portion of the insulating image. The insulating or nonconducting image layer or area is charged positively by the corona discharge needies when the developer powder carries an opposite tribolelectric charge, and the image layer is charged negatively when the developer powder carries an opposite triboelectric charge, so that when the image layer passes the outlet from the powder discharge receptacle and powder flows over the insulating image, it is attracted and adheres thereto so as to cover the image substantially and to form a powder image correspond- 6 ing to the image constitutin the insulating or nonconducting layer.

The desired result is attainable by supplying the corona discharge needles with a current hav ing a voltage peak between the charging needles and the insulating image layer of from 5000 to 8000 volts or higher. Any suitable high voltage source can be employed, either D. C., or rectified A. 0., the electrical mechanism being of convenient form to impose a high potential electrostatic charge on the insulating or nonconducting image layer.

The voltage necessary to effect a given charge on the plate varies with the size of the charging needles and the size of the needle points, a finer point needle requiring less voltage to effect the same charge on the plate that can be obtained with needles having points which are more blunt. The necessary voltage also varies with the spacing between adjacent needles and between the needle points and the plate, higher voltages he= ing necessary as the needles are spaced further apart or further from the printing plate.

With a rectified A. C. current having a peak voltage oi 5000 to 8000 volts for a negative charge, the needles are spaced .320" apart and spaced 1 5' from the plate or insulatin layer, while for a positive charge, satisfactory results are had with needles spaced .160" apart and spaced from the plate, the needles in either instance being spaced approximately the same distance from each other as they are from the plate. The separation of the electrode from the plate or paper is coordinated with the potential difference exist ing between the electrodes and plate or paper so that a practical maximum potential difference exists without danger of breakdown or sparking.

Instead of the corona charging needles illustrated in Figs. 1 and 2, it is possible to use a charging mechanism such as shown in Fig. 3 which includes a series of parallel wires.39, spaced from one another and suitably attached at their ends to blocks 4| of insulating material, mounted within a charging shield 42 which carries suit able lugs 43 by which the device may be fastened to the frame in such position that the wires 39 are located in proximity to the image -layer on the drum, spaced approximately therefrom, the wires 39 extending perpendicularly to the direction of travel'oi the insulating or nonconducting image and drum and being connected with a suitable source of current supply that furnishes the required high potential current.

The voltage required for the wire charging mechanism also varies with the diameter of the wires and the spacing of the wires from one another a'nd from. the image layer, a lower voltage being required for fine wires than for heavier wire and for wires positioned closer than where they are more distant from one another. Likewise, a lower voltage is required when the wires are arranged closer to the insulating image than when further away, and satisfactory results have been had with the wires separated from each other and from the insulatin image a distance oi. A as disclosed in copending application of John J. Rheinfrank, Serial No. 55,526, filed October 20, 1948.

The operation of the apparatus briefly i as follows:

The supply roll I9 is provided with a spool or supply of paper which is threaded upwardly between the charging needles 30 and the drum, thence laterally and downwardly over the chute 23 and around the receiving roll 24, and upon acvaoar placing a supply of developer powder-in the discharge receptacle II, the machine is ready for operation. Assuming that the printing plate with the insulating or nonconducting image layer thereon has been suitably fastened onto the drum, the machine is started by closing the circuit to the drive motor through a switch, not shown, whereupon the drum l starts to rotate in a counter-clockwise direction, developer powder is discharged from the receptacle H and gravitates downwardly over the insulating image layer on the drum as the latter rotates while at the same time the transfer strip is held against the drum and the image layer thereon by the electrostatic charge imposed by the charging needles 30. The insulating image having been charged by the electrostatic charging means, such as needles 3|] and 34, the developer powder adheres to the in sulating or nonconducting image layer and forms a powder image which is brought into contact with the transfer strip of paper or other material I8 held thereagainst by the electrostatic charge or attraction of the charged areas of the plate for the paper. The powder image is then transferred to the paper strip by the electrostatic action'of the charging needles 3!] as the image layer travels past the needles, the paper strip being thence deflected from the drum and fed downwardly over the chute 23 where the powder image is heated by the heating elements 31 sufficiently to fuse the powder onto the paper to produce a permanent image thereon, or the image may be fixed on the strip by a volatile solvent, or other acceptable means.

The major part of the powder forming the image is removed from the insulating layer and transferred onto the paper strip, and after leaving the paper strip, the insulating image layer is engaged by the cleaning device 38 to remove any surplus developer powder that may adhere to the surface of the image. This completes a cycle and the image layer is ready to receive another application of developer powder, it being understood that the image carried on the printing drum is reproduced on the transfer strip each time the drum completes one revolution, so that impressions of the image are repeatedly made on the transfer strip as fast as the drum is permitted to rotate.

In general, the speed of the drum and speed of production of the printed images on the paper strip is determined by the amount of time required to complete properly and effectively the several steps, namely, charging the image layer, applying developer powder to the image, transferring the image from the insulating layer to the transfer sheet, and cleaning the insulating image layer. On a machine such as disclosed herein, satisfactory results have been had upon rotating the drum and insulating or nonconducting image layer at a speed of 600 feet per minute, although higher speeds can be attained.

While the invention has been described with reference to the particular construction shown and in accordance with the procedure disclosed, it is not confined to the exact method and structural detail herein set forth, and this application is intended to cover such modifications or departures in the construction and method as may come within the purposes of the improvements or the scope of the following claims.

I claim:

1. The method of printing which consists in rotating a drum having an electrically charged image layer of electrically insulating or nonconducting material on an electrically grounded conducting surface, flowing a developer powder with a charge of polarity opposite to that of the charge onthe image layer over the image layer on one portion of the drum whereby said powder will adhere to the charged image layer and form a powder image, feeding a sheet of transfer material parallel to and in a path adjacent to a portion of the periphery of the drum carrying the powder image, and spraying an electrostatic charge from the side of the transfer material away from the periphery of the drum, onto the transfer material, said electrostatic charge being of opposite polarity to that of the charge on the powder, said electrostatic charge causing electrostatic action to hold said transfer material against said powder image and at the same time effect a transfer of the powder image from the image layer on the drum to the transfer material, stripping the trans fer material from the image layer and recharging the image layer from which the powder has been attracted.

2. The method of printing which consists in moving an electrically conductive support carrying an electrically charged image layer of electrically insulating or nonconducting material through a developing zone in which developer powder with a charge having a polarity opposite to that of the charge on the image layer is electrostatically deposited on the charged image layer to form a powder image, feeding a transfer material contiguous to the image layer carrying the powder image, spraying an electrostatic charge on the side of the transfer material away from the image layer adjacent the area of the transfer material contiguous with the powder image, said electrostatic charge being of opposite polarity to that of the charge on the powder and causing electrostatic action to hold said transfer material against said powder image and at the same time effect a transfer of the powder image from the image layer to the transfer material, stripping the transfer material from the image layer and recharging the image layer from which the powder image has been transferred.

3. A printing mechanism for transferring an electrically charged powder image to a surface comprising an electrically conducting rotatable printing drum having an image layer of electrically nonconducting material thereon, said image layer being charged electrostatically with a charge having a polarity Opposite to that of the polarity of the charge of the powder to be transferred,

cascading means located adjacent to the drum above the center at one side thereof, acting to flow developer powder with a charge of polarity opposite to that of the charge on the image layer over the charged image layer on one portion of the drum, said powder adhering to the image layer electrostatically to form a powder image, feeding means for a continuous strip of transfer material located away from the powder flowing area to supply transfer material to the printing mechanism, said transfer strip passing along a path contiguous to a portion of the periphery of the drum, an electrostatic charging means located adjacent to said path to effect a charge of opposite polarity to that of the charge on the powder and simultaneously acting to electrostatically attract the transfer strip against the image area thereby feeding the transfer material, and to effect transfer of the powder image to the transfer material, and to supply the electrostatic charge to the transfer material for recharging the image layer and means for stripping the electrostatically held paper from the image layer.

4. A printing mechanism for transferring a charged powder image to a surface comprising an electrically conducting movable support having an image layer of electrically nonconducting material thereon, said image layer being charged electrostatically with a charge having a polarity opposite to that of the polarity of the charge of the powder to be transferred, powder-applying means located adjacent to the movable support acting to flow developer powder charged with a charge of polarity opposite to that of the charge on the image layer over the charged image layer on one portion of the movable support, said powder adhering to the image layer electrostatically to form a powder image, feeding means for a strip of transfer material located away from the powder flowing area to supply transfer material to the printing mechanism, said transfer strip passing along a path contiguous to a portion of the image layer carried by the movable support, an electrostatic charging means located adjacent to said path to effect a charge on the transfer strip of opposite polarity to that of the charge on the powder and simultaneously acting to electrostatically attract the transfer strip against the image area thereby feeding the strip and to effect transfer of the powder image to the transfer material, and means for stripping the electrostatically held transfer material from the image layer to recharge the image area.

5. A printing mechanism for transferring a charged powder image to a surface comprising an electrically conducting rotatable printing drum having an image layer of electrically nonconducting material thereon, said image layer being charged electrostatically with a charge having a polarity opposite to that of the polarity of the charge of the powder to be transferred, powderapplying means located adjacent to the drum above the center at one side thereof, acting t flow developer powder charged with a charge of polarity opposite to that of the charge on the image layer over the charged image layer on one portion of the drum, said powder adhering to the image layer electrostatically to form a powder image, transfer material feeding means located away from the powder flowing area to supply transfer material to the printing mechanism, said transfer material passing along a path of contiguous to a portion of the periphery of the drum, an electrostatic charging means located adjacent to said path, to effect a charge of opposite polarity to that of the charge on the powder and simultaneously acting to electrostatically attract the transfer material against the image area thereby feeding the paper and to effect transfer of the powder image to the transfer material and to supply the electrostatic charge to the transfer maw 10 terial for recharging the image layer when the transfer material is stripped from the image and means for stripping the electrostatically held transfer material from the image layer.

6. A printing mechanism for transferring a charged powder image to a surface comprising an electrically conducting movable support having an image layer of electrically insulating or nonconducting material thereon, said image layer being charged electrostatically with a charge having a polarity opposite to that of the polarity of the charge of the powder to be transferred,-

powderapplying means located adjacent to the movable support above the center at one side thereof, acting to flow developer powder charged with a charge of polarity opposite to that of the charge on the image layer over the charged image layer, said powder adhering to the image layer electrostatically to form a powder image, transfer material feeding means located away from the powder flowing area to supply transfer material to the printing mechanism, said transfer material passing along a path contiguous to a portion of the periphery of the image layer carried by the movable support, an electrostatic charging means located adjacent to said path to effect a charge of opposite polarity on the transfer material to that of the charge on the powder and simultaneously acting to electrostatically attract the transfer material against the image area thereby feeding the transfer material and to effect transfer of the powder image to the transfer material and to supply the electrostatic charge to the transfer material for recharging the image layer when the transfer material is stripped from the image, and means for stripping the electrostatically held transfer material from the image layer.

ROLAND M. SCHAFFERT.

REFERENCES CITED The following references are of record in the file of this patent: 

